A roof tile produced from a hydraulic material such as mortar and concrete has been widely used as an architectural material in the world. Generally, a roof tile used as a roof material requires a lightweight property in terms of decreased structure strength, quake resistance and the like. However, if a roof tile is made thin for a lightweight property, there has been a problem that the roof tile has a lowered strength and an inferior durability.
Therefore, various proposals have been made for improving its strength while maintaining its lightweight property. For example, Patent Literature 1 proposes a lightweight concrete roof tile whose lightweight property and strength are improved by adding non-thixotropic silica fume and a dispersant for silica fume into a hydraulic material to form a reaction product of the non-thixotropic silica fume and lime. In addition, Patent Literature 2 discloses a lightweight concrete flat roof tile in which a fiber-mixed layer formed with mortar comprising mixed fibers and a mortar layer comprising no fibers are laminated.